Bacterial wilt (BW), caused by Ralstonia solanacearum, is one of the devastating diseases of tomatoes (Solanum lycopersicum L.). The use of resistant cultivars and breeding for genetic resistance is the most effective, economical, and environmentally friendly management strategy for this disease. It is necessary to screen diverse germplasm and cultivated genotypes to identify resistant resources and to develop resistant cultivars in tomatoes to combat the changing pathogen isolates. This study evaluated 40 United States Department of Agriculture (USDA) tomato accessions for their BW resistance to R. solanacearum isolate P822 under greenhouse conditions. The tomato plants were inoculated and visually assessed to observe symptoms and disease severity was scored on a scale of 0 to 4 (0 = no leaf wilted, 1 = 25% of leaves wilted, 2 = 50% leaves wilted, 3 = 75% of leaves wilted, 4 = 100% leaves wilted). Five accessions PI 645370, PI 647306, PI 600993, PI 355110, and PI 270210 were observed as BW resistance with PI 645370 showing the greatest resistance. The broad-sense heritability was estimated as 59.9% based on a 0-4 scale of disease incidence and 42.8% based on the disease severity index for BW resistance. Two distinct clusters (sub-populations) were detected among 39 of the 40 accessions, consisting of 3 and 2 BW resistant accessions in each cluster, respectively, suggesting differences in the genetic base in the five resistance accessions. The resistant accessions will contribute significantly to the tomato breeding program to develop new cultivars with BW resistance.

Bacterial wilt (BW), caused by Ralstonia solanacearum is one of the major biotic factors limiting tomato production in the humid tropics. Pyramiding of resistance genes through marker-assisted selection is an efficient way to develop durable BW resistant cultivars. Tomato line ‘Hawaii 7996’ (H7996) is a stable and robust resistance source against various R. solanacearum strains. Major BW resistance quantitative trait loci (QTLs) Bwr-12 and Bwr-6, and several minor or strain specific QTLs have been coarse-mapped in this line, but none has been fine-mapped and validated. The objective of the current study was to construct a high density genetic map using single-nucleotide polymorphism (SNP) markers derived from genotyping-by-sequencing, fine-map Bwr-12 and Bwr-6 and determine the effects of these QTLs using a near isogenic line (NIL) population. A high density genetic map using 1,604 SNP markers with an average distance of 0.82 cM was developed for 188 F9 recombinant inbred lines derived from the cross H7996 × WVa700. A total of seven QTLs associated with BW resistance to race 1-phylotype I or/and race 3-phylotype II strains were located on chromosomes 6 (Bwr-6.1, 6.2, 6.3 and 6.4) and 12 (Bwr-12.1, Bwr-12.2 and Bwr-12.3) with logarithm of odds (LOD) scores of 6.2-15.6 and 6.2-31.1, explaining 14.2-33.4% and 15.9-53.9% of the total phenotypic variation contributed from H7996, respectively. To validate the genetic effects of the two QTL regions, a set of 80 BC3F3 NILs containing different sections of Bwr-6 with or without Bwr-12 was phenotyped for disease severity after challenge with either race 1-phylotype I Pss4 or race 3-phylotype II Pss1632 BW strains over two seasons. Bwr-6.1 specific to Pss4 and Bwr-6.3 specific to Pss1632 were mapped to an interval of 5.0 cM (P < 0.05) between 6_33,444,000_SLM6-47 and 6_33,868,000_SLM6-124 SNP marker, and to 2.7 cM (P < 0.01) between positions 6_35,949,000 _SLM6-107 to 6_36,750,000_SLM6-82 marker, respectively. In addition, the specific effect of Bwr-12 for resistance to Pss4 (LOD score of 5.8-16.1, P < 0.01) was confirmed and markers for this QTL have already been made available previously.

The bacterial wilt pathogen, first known as Bacillus solanacearum, has undergone numerous taxonomic changes since its first description in 1896. The history and significance of this pathogen is covered in this review with an emphasis on the advances in technology that were used to support each reclassification that finally led to the current separation of Ralstonia solanacearum into three genomic species. Frequent name changes occurred as methodology transitioned from phenotypic, biochemical, and molecular studies, to genomics and functional genomics. The diversity, wide host range and geographical distribution of R. solanacearum has resulted in its inclusion in a “species complex” as genomic analyses of elucidated phylogenetic relationships among strains. Current advances in phylogenetics and functional genomics now open new avenues for research into the epidemiology and control of the devastating bacterial wilt disease.

Ralstonia solanacearum is the pathogen responsible for Ralstonia solanacearum, which is soil-borne, infests plant conduits to cause disease.They are not easy to control and are harmful.Therefore the development of a controlled-release agent responsive to the pathogen's soil temperature and moisture conditions could aid in its control. Corn kernel powder is used as a carrier for Tetramycin biopesticide, with various compounds tested for bonding.They were then made by extrusion moulding.Temperature and wetness responsive components, including Pentaerythritol Tetrastearate, Pentaerythritol Tetraoleate, Polyethylene Glycol Stearate, and Polyethylene Glycol Monooleate,are compounded and coated onto Tetramycin cores to form an intermediate shell layer. Finally, Ethyl cellulose(EC)and Hydroxypropyl methyl cellulose(HPMC) are dissolved and sprayed onto the outermost layer to complete the pellet's shell layer.After the evaluation of texture performance test,DSC analysis,TG test,temperature and humidity response performance test, as well as pellet cross-section SEM observation, field effectiveness test, etc., the preferred formulations were screened.The results showed that the preferred Core formulation:Corn kernel powder:Tetramycin aqueous:Xanthan gum mass ratio=13.5:23:2; Intermediate Shell layer:PETS: PETO: PEG400MO mass ratio=10:30:10; and Outer Shell layer: Ethyl cellulose (EC):Hydroxypropyl methyl cellulose (HPMC) mass ratio=5:1.Under soil conditions of high incidence of Ralstonia solanacearum, i.e., sustained warmth (30-35℃) and high humidity (30% moisture content), the formulated pills showed a release rate of 95.18% to 96.24% over a period of 35 days. Moreover, they showed a stepwise cyclic release process under alternating warm and humid-dry and cold conditions.In field tests on tobacco, a relative preventive efficacy of 54.74% was achieved 106 days post-transplanting. Soil bacterial community structure analysis revealed a significant decrease (2.28-2.84 times) in the abundance of Solanaceae Raelia under Tetramycin pellet treatment compared to the control. Additionally, fungal community structure showed highter consistency initially across various soil depths, with diversity differences between soil layers reestablished later (106 days), while the predominant categories of bacteria and fungi remained unchanged.In this study, we successfully developed a nucleoshell-type slow-controlled release pill embedded with Tetramycin. This pill effectively responded to temperature and humidity changes, resulting in high efficacy in disease prevention.This development holds significant promise for effectively improving drug utilization and easing application challenges, offering broad prospects for Ralstonia solanacearum prevention and control in agriculture.